1. Field of the Invention
The present invention relates to an image processor and an automated optical inspection system using the same, and more specifically to an automated optical inspection system for inspecting an appearance of a printed circuit board and the like, and an image processor used in the automated optical inspection system.
2. Description of Related Art
An image processor used in a conventional automated optical inspection system for inspecting an appearance of a printed circuit board and the like, includes an image memory circuit and an image processing circuit, for the purpose of inspecting a pin hole, an island, a projection, a partial dent, a breaking (disconnection), a bridge, a wire width thinning, a wire width thickening, a space reduction, etc. (as shown in FIG. 1A).
A first example of the conventional automated optical inspection system includes an image input device for sensing an image of an object to be inspected, and a feature recognition circuit for detecting a feature of a pattern such as a conductor pattern from the image data supplied from the image input device and for detecting a difference between the detected feature and a reference feature.
A second example of the conventional automated optical inspection system includes an image input device for sensing an image of an object to be inspected, an image memory circuit for storing an image data outputted from the image input device, and a central control circuit controlled by a control memory circuit for reading the image stored in the image memory circuit, one pixel by one pixel, and for scanning the read-out image in accordance with a predetermined procedure so as to find out any defect if it exists.
A third example of the conventional automated optical inspection system is such that a reference printed circuit board is sensed by an image input device, and a feature of the image of the reference printed circuit board is extracted by a feature recognition circuit and stored in a feature point image memory circuit. A printed circuit board to be inspected is sensed by the image input device, and a feature of the image of the printed circuit board to be inspected is extracted by the feature recognition circuit and compared in a feature comparing circuit with the feature of the image of the reference printed circuit board stored in the feature point image memory circuit, so that a defect is found if it exists.
A fourth example of the conventional automated optical inspection system includes an image input device, an image memory circuit, a central control circuit, a control memory circuit and an image processing circuit. The central control circuit is controlled by the control memory circuit for controlling to cause the image processing circuit to read the image data stored in the image memory circuit, to conduct a thinning and thickening and other necessary processing of the image and to write the result of the processing to the image memory circuit.
The above mentioned first and third examples of the conventional automated optical inspection system are advantageous since these examples can continuously process the images at a high speed. However, since a method of extracting the feature of the image is fixed to a simple way by a custom circuit for feature recognition, a correct shape very similar to a defect, for example, a space reduction at a contact between a land and a wiring conductor, has been often mistaken for a detect.
The second example of the conventional automated optical inspection system needs a long processing time for scanning the image, since the central control circuit reads out a control procedure from the control memory circuit at each time one pixel of the image is read out, and then generates a read address on the basis of the read-out control procedure.
The fourth example of the conventional automated optical inspection system also needs a long time for detecting a defect by the image processing, since only one image processing circuit is put into an operating condition at a time although many image processing circuits are provided.